1. Field of the Invention
The present invention relates to a color image processing apparatus which is suitable when applied to a simplified electrophotographic type color reproducing machine using a contact type image sensor.
2. Description of the Prior Art
There is known in the prior art a color image processing apparatus for optically reading image informations such as a document to record them on a sheet of recording paper by means of an electrophotographic type color reproducing machine.
In case the electrophotographic type color reproducing machine, the document containing color image informations is usually transformed into a plurality of color informations (including an achromatic color), on the basis of which are performed processes for forming an electrostatic latent image, developing the electrostatic image and fixing the developed image.
For these processes, an image pickup system 20 for picking up the document for frequent uses has a construction shown in FIGS. 19 and 20.
FIG. 19 shows an image pickup system in which the color image informations of the document are transformed into three primary color signals, i.e., red, green and blue color signals.
This pickup system 20 is constructed of first and second pickup subsystems 20A and 20B, as shown. The first pickup subsystem 20A is composed of a pair of prisms 21 and 22 and a dichroic mirror 25 to form a blue color separation image, which is focused on a pickup element 29 to output blue signals B.
The second pickup subsystem 20B is also composed of a pair of prisms 23 and 24 and a dichroic mirror 26. The optical image having passed through the first pickup subsystem 20A is extracted at the second pickup subsystem 20B into red and green color separation images. These red and green color separation images are then formed upon pickup elements 27 and 28, respectively, to output green signals G and red signals R.
The image pickup system 20 shown in FIG. 20 corresponds to the case of extraction into two color signals and is also constructed of the paired prisms 23 and 24 and a dichroic mirror 32. In the shown example, the image is separated into red and cyan color separation images by the dichroic mirror 32 so that red and cyan signals R and Cy are obtained from pickup elements 27 and 31, respectively.
Incidentally, in case the image signals are to be processed by using the image pickup system 20 thus constructed, color ghosts shown in FIGS. 21A and 21B would be produced in the constructions of FIGS. 19 and 20 unless the color extraction optical images were correctly formed in the normal positions of two or three pickup elements.
In order to eliminate the color ghosts, a plurality of pickup elements have to be stably positioned within a quarter pixel. In case, therefore, the pickup elements used have a pixel pitch of 7.mu., the mounting accuracy is required to be within 1 to 2.mu..
However, retention of such mechanical mounting accuracy is technically difficult, remarkably drops the yield of the image pickup system and causes the production cost-up.
In order to solve this problem, it is conceivable to use the image pickup system 20 using a contact type pickup element 43, as shown in FIG. 22.
Below a document 40 to be picked up, as shown in FIG. 22, there is arranged a light source such as a warm-white type fluorescent lamp 41 for illuminating the document 40. In the vicinity of the light source 41, there is disposed a SELFOC lens array (SLA) 42 which is arranged in parallel with the transverse direction (or the main scanning direction) of the document 40.
Moreover, the line-shaped pickup element (e.g., the contact type line sensor) 43 made of a CCD of the like is disposed in contact with a light guide which is formed in the lower face of that SLA 42.
Since the reflected light of the document 40 illuminates the pickup element 43 through the SLA 42, the color image of the document 40 is transformed into predetermined color image signals.
Incidentally, in case the contact type pickup element 43 is used in the image pickup system 20 to pickup the document 40, there is produced no color ghost due to the aforementioned mechanical mounting errors of the pickup element.
In order to separate the color image informations, however, there is attached to the front face of the pickup element 43 a color filter 45 which is composed in repetition of R, G and B as its units, for example, as shown in FIG. 23. As a result, the three small pixels R, G and B constitute one pixel.
If one pixel pitch is denoted as a, therefore, the small pixels are arranged with a mechanical pitch of a/3 so that the color ghosts similar to the aforementioned ones are produced.